1. Field of the Invention
The present invention concerns an optical rotary encoder for detecting the angle cf rotation of a rotatable pulse scale based on an angular signal in accordance with the angle of rotation and a reference position signal indicative of 0.degree. for the angle.
2. Description of the Prior Art
An optical rotary encoder has been used as a means for detecting the crank angle of an automobile engine, for example, in a case of controlling the ignition timing to a spark plug or in a case of varying the ignition timing in accordance with the number of rotations of the engine.
The optical rotary encoder of the prior art, as shown in FIG. 5 of the appended drawings, has a code pattern C.sub.1 for detecting an angle of rotation and a code pattern C.sub.2 for detecting a reference position formed in two concentric rows on a rotatable pulse scale 1 such that two kinds of optical pulse signals are respectively outputted.
Light is projected from two light-emitting devices 51 and 52 by way of two light-emitting optical fibers 53 and 54 into the code patterns C.sub.1 and C.sub.2, respectively. Then, optical pulse signals outputted from the patterns are sent by way of two light-receiving optical fibers 55 and 56 and then optoelectronically converted through respective photoreceiving devices 57 and 58, thereby causing these devices to detect an angular signal S.sub.1 and a reference position signal S.sub.2.
For instance, in a six-cylinder engine, a code pattern C.sub.2 is formed for judging respective cylinders such that the reference position signal S.sub.2 is outputted on every 60.degree. rotation of the pulse scale 1, and the timing for ignition is controlled depending on the number of pulses contained in the angular signal S.sub.1 after the input of the pulse of the reference position signal S.sub.2.
More specifically, a crank angle detected based on the angular signal S.sub.1 and the number of rotations of the engine detected based on the reference position signal S.sub.2 are inputted to an ignition system 60 for igniting each of spark plugs 63, 63, --- of the engine.
The ignition system 60 comprises a conversion table 61 for the number of rotations and the ignition timing, in which the crank angle indicative of the ignition timing for each of the cylinders corresponding to the engine rotation speed is previously set.
The ignition system also comprises a comparison means 62 for comparing the crank angle indicative of the ignition timing and the crank angle detected by the optical rotary encoder 1. In this system, the ignition timing for each of the cylinders corresponding to the rotation speed detected by the engine rotation speed sensor is outputted from the conversion table 61 for the number of rotations and the ignition timing, to the comparison means 62, and the comparison means 62 outputs a signal for igniting each of the spark plugs 63, 63, --- of the corresponding cylinder when the crank angle indicative of the ignition timing and the crank angle detected by the optical rotary encoder agree with each other.
The rotational shaft of the pulse scale 1 is connected with the crank shaft of an engine, while a control device 59 equipped with electronic parts sensitive to heat or vibrations such as light-emitting devices, 51, 52 and photoreceiving devices 57, 58 are disposed within the dashboard, in front of the driver's seat, remote from the engine, so that these devices are protected against direct affects of heat or vibrations from the engine.
However, if the light-emitting devices 51, 52, and the photoreceiving devices 57 and 58 are disposed each in pairs, since the light-emitting optical fibers 53, 54 and the light-receiving optical fibers 55, 56 have to be connected by means of respective optical connectors, which are each of a great diameter, it is difficult to accommodate the control device 59 in the narrow space behind an automotive dashboard.
Since the optical pulse signals outputted from a rotary encoder consist only of "1" and "0" signals, it is required to form two rows of code patterns on the pulse scale 1 and, correspondingly, two series of optical systems in order to obtain two kinds of information, that is, the angular signal and the reference position signal. This requires that the light-emitting devices 51, 52 and the photoreceiving devices 57, 58 be provided in twos, making it impossible to reduce the size of the connection portion of the device.
In addition, as the number of devices is increased, the number of relevant parts is also increased correspondingly, making the assembling work troublesome, as well as increasing the cost.